1. Field of the Invention
The present invention relates to clays and, more particularly, to a unique technique for maintaining low viscosity and preventing gelling of clay slurries stored or shipped for extended periods of time.
2. Description of the Prior Art
Refined clays are sold under certain required specifications such as brightness, particle-size distribution, viscosity, and the like. Because natural variations in the properties of crude clay are common, the crude clay ore is subjected to various known processing techniques, such as fractionation, delamination, treatment with chemical additives, leaching agents, flocculants, etc. A specific example of such a process is disclosed in U.S. Pat. No. 3,371,988. As disclosed in this patent, an aqueous clay suspension is contacted with a peptizing agent in an amount in excess of that required to maintain minimum viscosity and in an amount sufficient to remove titanium impurities and to improve the brightness of the clay. Further examples of known processes for refining or treating clays are disclosed in U.S. Pat. Nos. 3,320,027 and 3,442,677.
It is common practice in the industry to ship refined clay pigments to the customer as a dispersed high solids slurry. When shipping the clay slurry, the viscosity of the slurry increases, often in such a manner that after several days a thick mass or gel is formed. Obviously the gelled mass cannot be easily removed from the tank car. Thus, the customer may have to employ extensive mechanical means to redisperse the slurry or use various chemicals in order that the clay can be moved from the tank car. Often the tank car is returned to the manufacturer as being unacceptable. This increase in the viscosity and the formation of a gel has been found to occur even though a peptizing or dispersing aid has been added to the clay slurry prior to its shipment or storage. This dispersing agent would be in addition to that employed in the aforementioned U.S. Pat. No. 3,371,988, wherein the peptizing agent is employed in the refining of the clay itself.
Prior art proposals for stabilizing the viscosity of clay slurries or slips are disclosed in U.S. Pat. No. 3,341,340 and Canadian Pat. No. 854,271. These patents teach the use of high molecular weight polymeric materials or alkali metal salts of aminotrimethyl phosphonic acid to stabilize clay slurries.